Rory who? Caroline Wozniacki reaches her second ever Grand Slam decider in New York

Caroline Wozniacki of Denmark reacts against Shuai Peng of China during their women's singles semifinal match on Day 12 of the 2014 US OpenCaroline Wozniacki of Denmark looks on against Shuai Peng of China during their women's singles semi-final match on Day 12 of the 2014 US OpenShuai Peng of China grabs her leg after a play against Caroline Wozniacki of Denmark during their women's singles semifinal match on Day 12 of the 2014 US OpenCaroline Wozniacki of Denmark celebrates a point against Shuai Peng of China during their women's singles semifinal match on Day 12 of the 2014 US Open

Caroline Wozniacki has made it through to the US Open final after her opponent Peng Shuai retired with leg cramps in the second set of their semi-final at Flushing Meadows.

Wozniacki, who revealed she climbed off her own sick bed to play the match, was leading 7-6 (7/1) 4-3 when Peng began to struggle, apparently with severe cramp.

The Chinese player was initially helped off court and received a lengthy medical time-out but she managed to play only five more points before dropping to her knees on the court.

Peng eventually had to be helped away in a wheelchair, leaving Wozniacki to understandably muted celebrations of a huge achievement.

The 24-year-old said: "It was very difficult. You're out here and you want to battle and finish off properly. I just feel sorry for Peng, she played really well. It was really hot. Unfortunately she fell ill and I hope she'll be okay."

Wozniacki was given a pill by the doctor after the third game of the second set, and she said: "I'm feeling pretty good. I've been in bed the last two days. Thankfully I had two days off."

The Dane reached her only previous slam final in New York in 2009, losing to Kim Cllijsters.

"I have goose bumps right now," said Wozniacki, who will play either great friend Serena Williams or Russia's Ekaterina Makarova on Sunday.

"It's been five years since I've been in the final here so it's incredible to be back."

Peng, whose budding tennis career was almost ended by heart surgery when she was 12, had never even made a slam quarter-final in singles before this tournament.

But everything has clicked in New York and she reached the last four without having dropped a set.

Wozniacki had had a tougher route but her fourth-round win over Maria Sharapova in particular showed the 10th seed was at last ready to challenge for major titles again.

Hot and windy conditions made it tough for both players to play their best, and the defensive side of their games was on top in the first set.

Peng, who unusually plays double-handed off both sides, has the naturally more aggressive game and twice was a break ahead.

On the second occasion she served for the set at 6-5 but again Wozniacki hit straight back and then played a much more solid tie-break.

Wozniacki is running the New York Marathon in November and believes the training has helped her on the tennis court.

It was certainly a day for stamina to come to the fore but Peng stepped into the court more at the start of the second set and got her reward with a 2-0 lead.

For the third time, Wozniacki broke straight back and a run of four straight games put her in control of the match.

It was while Wozniacki served at 4-3 that Peng's problems began, and the match was halted with Wozniacki facing break point.

Despite the lengthy delay, the Dane was not awarded either a point or the game, which would have been the normal procedure if Peng's problems were solely cramp.

The Chinese player looked tearful when she returned to the court and the match ended amid distressing scenes with Peng clearly in agony.

In the four months since Rory McIlroy and Caroline Wozniacki parted ways, their sporting careers have reignited with Rory back at the top of the world ranking after back-to-back major victories in the Open Championship at Hoylake and the US PGA Championship at Valhalla and now Wozniacki is back at the top of her game and one win away from an elusive Grand Slam.